The present invention relates generally to automotive dampers or shock absorbers which receive mechanical shock. More particularly, the present invention relates to a unique hydraulic valve assembly which allows greater tunability of the shock absorber in both the mode of low speed or low hydraulic fluid flow and the mode of high speed or high hydraulic fluid flow.
Shock absorbers are used in conjunction with automotive suspension systems to absorb unwanted vibrations which occur during driving. To absorb these unwanted vibrations, shock absorbers are generally connected between the sprung portion (body) and the unsprung portion (wheels) of the automobile. A piston is located within a working chamber defined by a pressure tube of the shock absorber, with the piston being connected to the sprung portion of the automobile through a piston rod. The pressure tube is connected to the unsprung portion of the automobile by one of the methods known in the art. Because the piston is able, through valving, to limit the flow of damping fluid between opposite sides of the piston when the shock absorber is compressed or extended, the shock absorber is able to produce a damping force which damps the unwanted vibration which would otherwise be transmitted from the unsprung portion to the sprung portion of the automobile. In a dual tube shock absorber, a fluid reservoir is defined between the pressure tube and the reserve tube. When a full displacement piston valving system is used, the fluid reservoir is in direct communication with the lower portion of the working chamber defined by the pressure tube (the area below the piston). All damping forces produced by the shock absorber are the result of piston valving when a full displacement valving system is used. The greater the degree to which the flow of fluid within the shock absorber is restricted by the piston, the greater the damping forces which are generated by the shock absorber. Thus, a highly restricted flow of fluid would produce a firm ride while a less restricted flow of fluid would produce a soft ride.
In selecting the amount of damping that a shock absorber is to provide, at least three vehicle performance characteristics are considered. These three characteristics are ride comfort, vehicle handling and road holding ability. Ride comfort is often a function of the spring constant for the main springs of the vehicle as well as the spring constant for the seat and tires and the damping coefficient of the shock absorber. For optimum ride comfort, a relatively low damping force or a soft ride is preferred.
Vehicle handling is related to the variation in the vehicle""s attitude (i.e., roll, pitch and yaw). For optimum vehicle handling, relatively large damping forces, or a firm ride, are required to avoid excessively rapid variations in the vehicle""s attitude during cornering, acceleration and deceleration.
Finally, road holding ability is generally a function of the amount of contact between the tires and the ground. To optimize road handling ability, large damping forces, or a firm ride, are required when driving on irregular surfaces to prevent loss of contact between the wheel and the ground for excessive periods of time.
Various types of shock absorbers have been developed to generate the desired damping forces in relation to the various vehicle performance characteristics. Shock absorbers have been developed to provide different damping characteristics depending on the speed or acceleration of the piston within the pressure tube. Because of the exponential relation between pressure drop and flow rate, it is a difficult task to obtain a damping force at relatively low piston velocities, particularly at velocities near zero. Low speed damping force is important to vehicle handling since most vehicle handling events are controlled by low speed vehicle body velocities.
Various prior art systems for tuning shock absorbers during low speed movement of the piston create a low speed bleed orifice which provides a bleed passage which is always open across the piston. This bleed orifice can be created by utilizing orifice notches positioned in one or both of the compression and extension flexible discs adjacent to a respective sealing land in the piston or by utilizing orifice notches located directly on the respective sealing land itself. The limitations of these designs is that an orifice notch on the extension flexible disc or sealing land will affect the shock absorber during a compression stroke due to the fact that the orifice is always open. In a similar manner, an orifice notch on the compression flexible disc or sealing land will affect the shock absorber during an extension stroke due to the always open nature of the orifice.
The continued development of shock absorbers includes the development of low speed tunability systems which can separate the compression low speed tuning from the extension stroke and/or separate the extension low speed tuning from the compression stroke. The separation of these tuning systems allows the damper designer the ability to tune each system independently of the other system.
The present invention provides the art with a method for isolating the compression bleed system from the extension stroke and/or for isolating the extension bleed system from the compression stroke. The present invention provides a floating port blocker disc that fits in the pressure area/channel of the piston valves. Neither the inside or outside diameters of the floating port blocker disc are fixed. Thus, the disc is free to float within the channel to allow the bleed flow in one direction but to act as a check valve for prohibiting fluid flow in the opposite direction. In addition, the floating port blocker disc provides high speed port restriction that is a function of pressure. Thus, the port blocker disc acts as a variable high speed orifice.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.